The present invention relates to an optical disk readout method and optical disk readout system, and in particular, to an optical disk readout method and optical disk readout system configured such that separate light beams simultaneously illuminate each of the multiple adjacent tracks of an optical disk in which tracks are formed in a spiral (e.g. CD-ROM, CD-WO, DVD, DVD-ROM, or DVD-RAM disk), and wherein data recorded in the tracks being illuminated by the beams is read from the detected output of each returned beam by a record data readout system.
One technique available as a method for reading recorded data from CD-ROM at high speed is the multi-beam technique. This multi-beam technique is disclosed in U.S. Pat. No. 5,457,670 and PCT Gazette WO94/19797 (PCT/US94/01790). In this technique, separate light beams simultaneously illuminate each of the multiple adjacent tracks of an optical disk on which the tracks are formed in a spiral. Data recorded in the tracks illuminated by the beams is simultaneously read-back from the detected output of each returned beam by a record data readout system in a manner such that there will be no duplications or gaps in the data being read back, and such that the data will be output in the sequence in which it was recorded.
Such a multi-beam optical disk (CD-ROM) readout method will be described with reference to FIG. 20. Item 1 is a CD-ROM as seen from the signal side (optical pickup side), on which tracks in which data has been recorded are formed in a spiral with the outside diameter (outer circumference) of the tracks shown at the top of FIG. 20, and the inside diameter (inner circumference) at the bottom. Item 2 is an optical pickup capable of emitting five light beams. When reading, the optical pickup 2 is in a state of relative rotation with respect to the CD-ROM 1, gradually moving from the inside of the disk toward the circumference as it advances, reading the recorded data as proceeds. Now, when the optical pickup 2 arrives at position I and starts reading data, the tracks xc3x97 through (x+4) are separately illuminated simultaneously by the light beams 31-35, respectively. The data recorded in each of the tracks illuminated by the beams 31-35 is simultaneously read from the detected output of each of the returned beams by the prescribed record data readout system, and the data recorded on the CD-ROM 1 is output serially in the sequence in which it was recorded, with no duplications or gaps.
The recorded data of CD-ROM 1 is structured in accordance with a CD signal format in sub-code Q-channel A-time (absolute time) frame units, where one frame={fraction (1/75)} second. Hereinafter, A-times are expressed in the form aa:bb:cc, where aa=seconds, bb=minutes, and cc=frames. If the optical pickup 2 were to start reading data from position I of FIG. 20, then
the light beam 31 channel would start reading recorded data correctly from the A-time=23:40:60 portion;
the light beam 32 channel would start reading recorded data correctly from the A-time=23:41:00 portion;
the light beam 33 channel would start reading recorded data correctly from the A-time=23:41:15 portion;
the light beam 34 channel would start reading recorded data correctly from the A-time=23:41:30 portion; and
the light beam 35 channel would start reading recorded data correctly from the A-time=23:41:45 portion.
By the time the CD-ROM 1 completes approximately (slightly more than) one revolution, advancing the optical pickup 2 to position II of FIG. 20 (where tracks (x+1)-(x+5) are illuminated by light beams 31-35 respectively,
the light beam 31 channel will have read the recorded data correctly up to A-time=23:40:74;
the light beam 32 channel will have read the recorded data correctly up to A-time=23:41:14;
the light beam 33 channel will have read the recorded data correctly up to A-time=23:41:29; and
the light beam 34 channel will have read the recorded data correctly up to A-time=23:41:44;
with the gaps between the data read separately by the light beams 31-35 now filled. (By this time, light beam 35 will have read the recorded data correctly up to A-time =23:41:59.) The data read by light beams 31-35 is then output from the system in the sequence in which it was recorded, such that no duplications occur.(No frame is output more than once.)
When the optical pickup 2 has read data as far as position II in FIG. 20, the light pickup 2 is xe2x80x9ctrack-jumpedxe2x80x9d forward (outward from the center of the CD-ROM 1) by three tracks. This puts the light pickup 2 in position III of FIG. 20 (where light beams 31 through 35 now illuminate tracks (x+4) through (x+8), respectively). At that point, the read operation then begins again, with
the light beam 31 channel reading recorded data correctly from the A-time=23:41:48 portion;
the light beam 32 channel reading recorded data correctly from the A-time=23:41:63 portion;
the light beam 33 channel reading recorded data correctly from the A-time=23:42:03 portion;
the light beam 34 channel reading recorded data correctly from the A-time=23:42:18 portion; and
the light beam 35 channel reading recorded data correctly from the A-time=23:42:33 portion.
By the time the CD-ROM 1 turns approximately (slightly more than) one revolution, advancing the optical pickup 2 to position IV of FIG. 20 (where tracks (x+5)-(x+9) are illuminated by light beams 31-35 respectively)
the light beam 31 channel will have read the recorded data correctly up to A-time=23:41:62;
the light beam 32 channel will have read the recorded data correctly up to A-time=23:42:02;
the light beam 33 channel will have read the recorded data correctly up to A-time=23:42:17; and
the light beam 34 channel will have read the recorded data correctly up to A-time=23:42:32: and
with all gaps between the data read by light beams 31-35 now closed. (By this time, light beam 35 will have read the recorded data correctly up to A-time=23:42:47.) The data read by light beams 31-35 is then output from the system in the sequence in which it was recorded, and such that no duplications occur.
As the optical pickup 2 advances from position I to position II (one revolution of the CD-ROM 1), the optical beam 35 channel reads recorded data from A-time 23:41:45 through 23:41:59. As the optical pickup 2 advances from position III to position IV (one revolution of the CD-ROM 1), the optical beam 31 channel reads recorded data from A-time 23:41:48 through 23:41:62. In other words, there is an overlap between A-times 23:41:48 and 23:41:59, which was read by both channels. To avoid outputting these 12 frames twice, the system outputs only the copy of this data that was read by the 35 channel (which read it first) and discards the duplicate data read by channel 31.
Moreover, when the track jump from position II of FIG. 20 is executed, instead of a four-track jump, a three-track jump is executed. Thus the data in track (x+4), which was being read by the light beam 31 channel before the jump, is now illuminated by light beam 31. The reason for doing this is that a four-track jump would have put the optical pickup 2 in position III of FIG. 20. The light beam 31 channel would then have resumed reading recorded data from A-time 23:41:63. This would have left a gap in the data between 23:41:60 and 23:41:62, which had not yet been read by the light beam 35 channel prior to the track jump.
Stated in general terms, for a system with n light beams, where n is an integer of 3 or greater, each light beam channel reads data for approximately one revolution. At that point, a forward track jump of (nxe2x88x922) tracks is executed, after recorded data is again read for approximately one revolution. This operation repeats continuously to perform high-speed readout of the CD-ROM 1.
Due to factors such as track pitch variance, surface flutter, and eccentric wobble of the CD-ROM 1, however, some of the recorded data may not be readable by the light beam circuits. Consider a disk readout system such as the prior art method described above, where n light beam channels read approximately one revolution-worth of data, then a forward track jump of (nxe2x88x922) tracks is executed, after which approximately one revolution of recorded data is again read, and this operation is repeated. In this method, for the case illustrated in FIG. 20, if the recorded data in the light beam channel 32, for example, became unreadable during the approximately one revolution of optical pickup 2 reading from the position I of FIG. 20, the data from A-time 23:41:00 through 23:41:14 would be lost.
When the optical pickup 2 reaches position II, it jumps three tracks to position III; therefore, this data between A-time=23:41:00 and A-time=23:41:14 is never read. Next, as the recorded data read continues for approximately one revolution from position III, the recorded data between A-time=23:41:63 and A-time=23:42:02 fails to be read.
In this method, then, there was a problem in that some data required by the user could not be retrieved.
In consideration of the above problem of the prior art, it is an object of the present invention to provide an optical disk readout method and optical disk readout system in which, even if recorded data cannot be read by some of the light beams, the required data can still be obtained.
It is also an object of the present invention to provide an optical disk readout method and optical disk readout system capable of reading data from an optical disk more efficiently.
In an optical disk readout method according to the present invention, n adjacent tracks (n being an integer of 3 or greater) of an optical disk are illuminated simultaneously by separate n light beams arranged in the radial direction of the optical disk in order to read recorded data in the tracks illuminated by the n light beams, from output obtained by detecting returned ones of the n light beams through n light beam-read channels, and the reading of the optical disk is performed by alternating between a continuous reading and a track jump in the forward direction.
The method is characterized by steps of detecting the alignment status in the radial direction for the light beam-read channels incapable of reading recorded data from the optical disk; designating of light beam-read channels to be used for reading and determining the number of tracks to be jumped, according to the detection for the alignment status in the radial direction of the capable light beam-read channels; storing the readout data and corresponding frame addresses of the optical disk during the continuous reading by the light beam-read channels designated for reading; and executing the track jump by the determined number of tracks when the stored corresponding frame addresses become successive for data from the designated light beam-read channels during the continuous reading.
In the embodiment, when detecting that one or adjacent two light beam-read channels only are capable of reading the recorded data, a single light beam-read channel is designated for reading and the continuous reading is successively conducted without executing the track jump.
M is the number of beams in the most populous contiguous group of light beam-read channels from which data can be read, said M light beam-read channels are designated as the valid ones, and the optical disk is read by alternating between performing continuous reading through said M designated valid light beam-read channels, for approximately one revolution of the optical disk, and executing a track jump of (Mxe2x88x922) tracks in the forward direction.
If Q is the distance, in number of tracks, between the innermost and outermost beams of light beam-read channels capable of reading recorded data, R is the number of beams in the most populous contiguous group of light beam-read channel incapable of reading recorded data, whose beams lie between said innermost and outermost light beams, and also if Q is at least 2, and R is at least 1, then the optical disk is read by alternating between performing continuous reading of the optical disk through the light beam-read channels that are capable of reading recorded data for approximately (R+1) revolutions of the optical disk, and executing a track jump of (Qxe2x88x921) tracks in the forward direction.
When (Qxe2x88x921) is equal or less than zero, a single light beam-read channel only is designated for reading and the continuous reading is successively performed without executing the track jump.
In an optical disk readout apparatus according to the present invention, n adjacent tracks (n being an integer of 3 or greater) of an optical disk are illuminated simultaneously by separate n light beams arranged in the radial direction of the optical disk, comprising optical detection means for reading recorded data in the tracks illuminated by the n light beams, from output obtained by detecting returned ones of the n light beams through n light beam-read channels, and readout control means for reading the optical disk by alternating between a continuous reading and a track jump in the forward direction.
The apparatus is characterized by means for detecting the alignment status in the radial direction for the light beam-read channels incapable of reading recorded data from the optical disk; means for designating of light beam-read channels to be used for reading and for determining the number of tracks to be jumped, according to the detection for the alignment status in the radial direction of the capable light beam-read channels; and means for storing the readout data and corresponding frame addresses of the optical disk during the continuous reading by the light beam-read channels designated for reading; wherein the readout control means executes the track jump by the determined number of tracks when the stored corresponding frame addresses become successive for data from the designated light beam-read channels during the continuous reading.